1. Technical Field of the Invention
The present invention relates to a phosphor composition, a phosphor paste, and a photosensitive dry film. More particularly, the present invention relates to a phosphor composition comprising a blue-emitting inorganic phosphor, which, when used in the formation of a phosphor layer in a plasma display panel (PPD.), can solve a problem of lowered brightness involved in the phosphor layer, a phosphor paste comprising the composition, and a photosensitive dry film formed from the paste.
2. Background Art
In general, PPD. Comprises two opposed glass substrates, a pair of electrodes systematically arranged in the glass substrates, and a gas (mainly neon or the like) sealed therebetween. A voltage is applied across the electrodes to produce discharge within minute cells around the electrodes to emit light from each cell, thereby displaying information. Systematically arranged cells are selectively subjected to discharge luminescence in order to display information. Such PAPS are classified into two types; a direct current type PPD., wherein electrodes are exposed to a discharge space (DC type), and an alternating current type (AC type) wherein electrodes are covered with an insulating layer. Each of these types is further classified into a refresh drive system and a memory drive system according to display functions and drive systems.
FIG. 1 is an embodiment of the construction of an AC type PPD. In the drawing, a front plate 11 and a back plate 12 are shown separately from each other. As shown in the drawing, the glass front plate 11 and the back plate 12 are arranged parallel and opposite to each other. Barrier ribs 13 are provided so as to stand in a fixed state on the back plate 12 in its front surface side, and the front plate 11 and the back plate 12 are held while leaving a given distance between the front plate 11 and the back plate 12 by means of the barrier ribs 13. Composite electrodes each comprising a sustaining electrode 14 as a transparent electrode and a bus electrode 15 as a metallic electrode are provided parallel to each other on the front plate 11 in its back plate side, and a dielectric layer 16 is provided so as to cover the composite electrode. Further, a protective layer 17 (MgSO layer) is provided on the surface of the dielectric layer 16.
On the other hand, address electrodes 18 are provided between the barrier ribs 13 on the back plate 12 in its front surface side so that the address electrodes 18 are parallel to each other and orthogonal to the composite electrodes. Further, a phosphor layer 19 is provided so as to cover the wall surface of the barrier ribs 13 and the bottom face of cells.
In the AC type PPD., a predetermined voltage is applied, from an alternating-current power supply, across the composite electrodes on the front plate 11 to create an electric field, thereby producing discharge in each cell as a display element defined by the front plate 11, the back plate 12, and the barrier ribs 13. Ultraviolet light produced by the discharge permits the phosphor layer 19 to emit light, and light passed through the front plate 11 is viewed by an observer.
Methods for coating the phosphor layer proposed in the art include (1) printing a phosphor-containing paste by silk screen and baking the print, (2) rendering the phosphor paste photosensitive and forming the phosphor layer from the phosphor paste by photolithography, and (3) a photoresist film of a photosensitive resin composition.
In all the above methods, firing at a temperature suitable for avoiding the occurrence of a residue of any organic material in the final phosphor layer is carried out to form a phosphor layer. This firing step poses a problem of lowered sensitivity (brightness) of phosphor. This problem more or less occurs in any phosphor of red, green, and blue. This tendency is particularly significant for the blue phosphor, especially when the phosphor layer is formed by photolithography. Consequently, a PPD. Back plate having satisfactory properties cannot be provided.
Accordingly, it is an object of the present invention to provide a blue phosphor composition, a phosphor paste, and a photosensitive dry film that can solve the above problems of the prior art and can yield a phosphor layer that causes no significant lowering in brightness upon firing.